There is a rack structure having a heat shielding plate disposed between upper and lower shelves in which air increased of its temperature due to being used to cool the lower shelf is discharged along a partition plate of the heat shielding plate such that the heated air does not affect the upper shelf.
Furthermore, there is a disk array device having a mechanism in which an opening area of a vent hole of a back board is adjusted in such a manner that when a unit on which a hard disk drive is mounted is mounted, the vent hole is opened and when a unit on which a hard disk drive is mounted is not mounted, the vent hole is closed.
International Publication Pamphlet No. WO 2006/054332 and Japanese Laid-open Patent Publication No. 2006-059448 are reference documents.